Linq to sql Class member is unmapped

I am creating ASP.Net web application (.Net Framework) with individual authentication having those projects: 1- Domain project containing base class:

public class IdentityUser<TKey, TUserLogin, TUserRole, TUserClaim> : IUser<TKey>
                                                                    where TUserLogin : IdentityUserLogin<TKey>
                                                                    where TUserRole : IdentityUserRole<TKey>
                                                                    where TUserClaim : IdentityUserClaim<TKey>
    {
        public virtual TKey Id { get; set; }
        public virtual string UserName { get; set; }
        public virtual string PasswordHash { get; set; }
        public virtual string SecurityStamp { get; set; }

    }

2- DAl Project containing user Class

[TableAttribute(Name = "dbo.IdentityUsers")]
public partial class IdentityUser: IdentityUser<string, IdentityUserLogin, IdentityUserRole, IdentityUserClaim>,
                                   INotifyPropertyChanging, INotifyPropertyChanged
{

private static PropertyChangingEventArgs emptyChangingEventArgs = new PropertyChangingEventArgs(String.Empty);
public event PropertyChangingEventHandler PropertyChanging;
public event PropertyChangedEventHandler PropertyChanged;

private string _Id;
[ColumnAttribute(Name = "Id", Storage = "_Id", DbType = "NVarChar(128) NOT NULL", CanBeNull = false, IsPrimaryKey = true, UpdateCheck = UpdateCheck.Never)]
public override string Id
{
    get
    {
        return _Id;
    }
    set
    {
        if ((_Id != value))
        {
            OnIdChanging(value);
            SendPropertyChanging();
            _Id = value;
            SendPropertyChanged("Id");
            OnIdChanged();
        }
    }
}

private string _UserName;
[ColumnAttribute(Name = "UserName", Storage = "_UserName", DbType = "NVarChar(256) NOT NULL", CanBeNull = false, UpdateCheck = UpdateCheck.Never)]
public override string UserName
{
    get
    {
        return _UserName;
    }
    set
    {
        if ((_UserName != value))
        {
            OnUserNameChanging(value);
            SendPropertyChanging();
            _UserName = value;
            SendPropertyChanged("UserName");
            OnUserNameChanged();
        }
    }
}

private string _PasswordHash;
[ColumnAttribute(Name = "PasswordHash", Storage = "_PasswordHash", DbType = "NVarChar(MAX)", UpdateCheck = UpdateCheck.Never)]
public override string PasswordHash
{
    get
    {
        return _PasswordHash;
    }
    set
    {
        if ((_PasswordHash != value))
        {
            OnPasswordHashChanging(value);
            SendPropertyChanging();
            _PasswordHash = value;
            SendPropertyChanged("PasswordHash");
            OnPasswordHashChanged();
        }
    }
}

private string _SecurityStamp;
[ColumnAttribute(Name = "SecurityStamp", Storage = "_SecurityStamp", DbType = "NVarChar(MAX)", UpdateCheck = UpdateCheck.Never)]
public override string SecurityStamp
{
    get
    {
        return _SecurityStamp;
    }
    set
    {
        if ((_SecurityStamp != value))
        {
            OnSecurityStampChanging(value);
            SendPropertyChanging();
            _SecurityStamp = value;
            SendPropertyChanged("SecurityStamp");
            OnSecurityStampChanged();
        }
    }
}

public IdentityUser()
{
    _Id = Guid.NewGuid().ToString();
}

public IdentityUser(string userName) : this()
{
    _UserName = userName;
    }

}

and DataContext Class

[Database]
public class MahrousSoftDataContext : DataContext
{

#region Members

private static MappingSource mappingSource = new AttributeMappingSource();

#endregion Members


#region Properties

public Table<IdentityUser> IdentityUsers
{
    get
    {
        return GetTable<IdentityUser>();
    }
}

#endregion Properties


#region Constructors

public MahrousSoftDataContext() :
        base(System.Configuration.ConfigurationManager.ConnectionStrings["mamsdbConnectionString"].ConnectionString, mappingSource)
{
    OnCreated();
}

public MahrousSoftDataContext(string connection) : base(connection, mappingSource)
{
    OnCreated();
}

public MahrousSoftDataContext(System.Data.IDbConnection connection) : base(connection, mappingSource)
{
    OnCreated();
}

public MahrousSoftDataContext(string connection, MappingSource mappingSource) :
        base(connection, mappingSource)
{
    OnCreated();
}

public MahrousSoftDataContext(System.Data.IDbConnection connection, MappingSource mappingSource) :
        base(connection, mappingSource)
{
    OnCreated();
}

#endregion Constructors

}

3- BLL Project containing usermanger and applicationusermanger

4- web project

the problem is when i register a new user i get this exception

System.InvalidOperationException occurred HResult=0x80131509 Message=Class member IdentityUser`5.UserName is unmapped. Source= StackTrace:

  at System.Data.Linq.Mapping.AttributedMetaType.GetDataMember(MemberInfo mi)

at System.Data.Linq.CommonDataServices.GetKeyFromPredicate(MetaType type, Dictionary2 keys, Expression mex, Expression vex) at System.Data.Linq.CommonDataServices.GetKeysFromPredicate(MetaType type, Dictionary2 keys, Expression expr) at System.Data.Linq.CommonDataServices.GetKeyValues(MetaType type, LambdaExpression predicate) at System.Data.Linq.CommonDataServices.GetCachedObject(Expression query) at System.Data.Linq.SqlClient.SqlProvider.GetCachedResult(Expression query) at System.Data.Linq.SqlClient.SqlProvider.System.Data.Linq.Provider.IProvider.Execute(Expression query) at System.Data.Linq.Table1.System.Linq.IQueryProvider.Execute[TResult](Expression expression) at System.Linq.Queryable.Single[TSource](IQueryable1 source, Expression1 predicate) at MA.MahrousSoft.DAL.Tables.Identity.IdentityUserTable1.SelectByUserName(MahrousSoftDataContext db, String username) in IdentityUserTable.cs:line 26 at MA.MahrousSoft.Stores.Identity.IdentityUserStore1.FindByNameAsync(MahrousSoftDataContext db, String userName) in IdentityUserStore.cs:line 57 at MA.MahrousSoft.Stores.Identity.IdentityUserStore1.FindByNameAsync(String userName) in IdentityUserStore.cs:line 48 at Microsoft.AspNet.Identity.UserManager2.FindByNameAsync(String userName) at Microsoft.AspNet.Identity.UserValidator2.d__4.MoveNext()